In the semiconductor device such as a power module and a LED, it has a structure in which the semiconductor element is bonded onto a circuit layer composed of a conductive material.
Since a power semiconductor device of high-power control that is used to control wind power, electric vehicles such as electric automobiles, and the like, generates a large amount of heat, as a substrate mounting the power semiconductor device, in the case where a metal plate having excellent conductivity is bonded to one surface of a ceramic substrate (insulation layer) composed of, for example AN (aluminum nitride), or two metal plates having excellent conductivity are bonded to respective surfaces of the ceramic substrate, a power module substrate in which the metal plate disposed on one surface of the ceramic substrate is used as a circuit layer and another metal plate disposed on the other surface of the ceramic substrate is used as a metal layer has been widely used conventionally.
For example, in the power module shown in Patent Document 1, it has a structure including: a power module substrate in which a circuit layer (aluminum member) composed of Al and disposed on one surface of a ceramic substrate, and a metal layer composed of Al and disposed on the other surface of the ceramic substrate are formed; and a semiconductor device bonded on the circuit layer with a solder material interposed therebetween. A heat sink is bonded to the downside of the power module substrate, and the power module is configured to transfer the heat generated by the semiconductor device to the power module substrate side and to dissipate the heat to the outside via the heat sink.
As in the power module described in the Patent Document 1, when the circuit layer is composed of Al, an oxidation coating film of Al is formed on a surface of the circuit layer, and therefore, the semiconductor device cannot be bonded by the solder material. Also, when the metal layer is composed of Al, an oxidation coating film of Al is formed on a surface of the metal layer, and therefore, the heat sink cannot be bonded by the solder material.
Conventionally, as shown in, for example, Patent Document 2, a Ni plating film is formed on each surface of a circuit layer, metal layer and heat sink by electroless plating or the like, and then, they are bonded together by a solder material.
In addition, in Patent Document 3, as an alternative technique using the solder material, a technique in which a semiconductor device, metal layer, heat sink and so on are bonded together using a silver oxide paste that includes silver oxide particles and a reducing agent containing an organic substance has been proposed.
Furthermore, in Patent Document 4, a power module in which each of a circuit layer and metal layer is formed by an Al layer and Cu layer has been proposed. In this case, since the Cu layer is disposed on each surface of the circuit layer and metal layer, a good bonding of the semiconductor device can be performed using the solder material. Also, since Cu has a large deformation resistance as compared with Al, when a heat cycle is applied on the power module, a great deformation of the surface of the circuit layer and the surface of the metal layer can be prevented, the occurrence of cracks in a solder layer is prevented, and the bonding reliability between the semiconductor device and the circuit layer and the bonding reliability between the metal layer and the heat sink can be improved.
In addition, in the power module described in Patent Document 4, a bonding body in which an Al layer and Cu layer are bonded together with a Ti layer interposed therebetween is used as the circuit layer and the metal layer. Here, a diffusion layer is formed between the Al layer and Ti layer, and the diffusion layer has an Al—Ti layer, an Al—Ti—Si layer, and an Al—Ti—Cu layer such that the Al—Ti layer, Al—Ti—Si layer, and Al—Ti—Cu layer are sequentially arranged from the Al layer.